In the mobile communication field, attentions are recently drawn to the wireless communication technology based on impulses, called UWB (Ultra Wide Band), as a communication scheme to realize high speed and low consumption power.
PPM (pulse position modulation) modulation and bi-phase modulation are known as UWB basic modulation schemes. PPM modulation is UWB modulation based on the string of equally spaced impulses, which is of a modulation scheme using impulses positioned deviated slight with respect to the equally spaced interval (time hopping). Concerning PPM modulation, generally there is known a demodulation scheme based on the correlation of waveform to a template (e.g. see a document of Nikkei Electronics, Aug. 26, 2002 No. 829, p. 137-144 “Reason of High Speed Transmission in Ultra Wideband”). Bi-phase modulation is of a modulation scheme based on sign inversion though using a string of equally spaced impulses.
FIG. 1 is an example of a UWB transceiver based on PPM modulation described in the above described document. In the transmitter, a clock generating section 1000 generates a clock pulse 1001 at a regular interval so that a delay section 1002 provides it with a delay corresponding to a transmission data signal 1003. In the timing, a transmission-wave generating section 1004 generates an impulse to thereby transmit a PPM modulation signal at a transmission antenna 1005.
The receiver, a template-waveform generating section 1009 generates a template 1010, in the timing of a clock pulse 1008 generated at the clock generating section 1007. The signal received at a reception antenna 1006 is taken a correlation to the template 1010 by means of a pulse correlator 1011. The correlation result obtained is integrated and demodulated by an integrating section 1012.
The UWB communication scheme configured as above has the following merits, as compared with the conventional communication scheme using the carrier wave.
(1) Low Consumption Power
Less power is required because of a scheme not using a carrier wave always needing a continuous output. This enables to reduce the apparatus consumption power.
(2) Small Size and Low Price
Analog RF components are unnecessary which make it difficult to fabricate a CMOS-based integrated circuit, such as VCOs, RF filters, etc. Furthermore, exact linearity is not needed for the circuit. Accordingly, the scheme is well suited for integrated circuit fabrication, thus facilitating to reduce the size and price of apparatus.
(3) High-Speed Communications
Frequency band is significantly broad because impulses are used in communications, enabling high-speed data communications. In the UWB communications using the microwave band (3 GHz-10 GHz), data communications are available at a rate as high as approximately 100 Mbps.
Nevertheless, because the template waveform generating section 1009 of FIG. 1 is required to generate an exact impulse waveform on the order of nanoseconds, it must be configured on a circuit extremely high in speed requiring linearity. This makes it impossible to make use of the superiority in respect of low power consumption and apparatus low price, a merit in the UWB communication scheme.
Meanwhile, in the circuit of FIG. 1, demodulation is impossible to carry out on both PPM modulation and bi-phase modulation at the same time.
Furthermore, the UWB demodulation scheme, broad in service band, involves a problem of not resistive to interferences of from other wireless communication systems included within the band.